Equilibrium and stability of supermassive stars in binary systems

Shibata, Masaru; Shapiro, S. L.; Uryū, Kōji

doi:10.1103/physrevd.64.024004

Cited by 35 publications

(92 citation statements)

References 30 publications

(60 reference statements)

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“…Moreover, the new results given by them in Refs. [46,65] for the case of γ = 2 agrees with ours at the order of 10 −3 , while being slightly smaller than our result as expected. …”

Section: Comparison With Previous Numerical Resultssupporting

confidence: 80%

“…[37], we have compared for end point configurations only and listed the results in Table I. In the same table, results of Shibata and Uryu [46] are also given for comparison in the case γ = 2. It is found that the ADM mass agree with each other at the order of 10 −3 , and that the orbital angular velocity as well as the total angular momentum agree at a few %.…”

Section: Comparison With Previous Numerical Resultsmentioning

confidence: 99%

“…[46,65]. TABLE II: Orbital angular velocity, ADM mass, total angular momentum, virial errors, axial ratios, relative change in central energy density, and the cusp indicator χ along constant baryon number sequences of identical mass binaries in synchronized motion, for various compactness.…”

Section: Discussionmentioning

confidence: 99%

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Various features of quasiequilibrium sequences of binary neutron stars in general relativity

2003

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Quasiequilibrium sequences of binary neutron stars are numerically calculated in the framework of the Isenberg-Wilson-Mathews (IWM) approximation of general relativity. The results are presented for both rotation states of synchronized spins and irrotational motion, the latter being considered as the realistic one for binary neutron stars just prior to the merger. We assume a polytropic equation of state and compute several evolutionary sequences of binary systems composed of different-mass stars as well as identical-mass stars with adiabatic indices γ = 2.5, 2.25, 2, and 1.8. From our results, we propose as a conjecture that if the turning point of binding energy (and total angular momentum) locating the innermost stable circular orbit (ISCO) is found in Newtonian gravity for some value of the adiabatic index γ0, that of the ADM mass (and total angular momentum) should exist in the IWM approximation of general relativity for the same value of the adiabatic index.

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“…Moreover, the new results given by them in Refs. [46,65] for the case of γ = 2 agrees with ours at the order of 10 −3 , while being slightly smaller than our result as expected. …”

Section: Comparison With Previous Numerical Resultssupporting

confidence: 80%

Section: Comparison With Previous Numerical Resultsmentioning

confidence: 99%

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Various features of quasiequilibrium sequences of binary neutron stars in general relativity

2003

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“…For L < ∼ 0.4λ, the amplitude and the radiation reaction of gravitational waves are significantly overestimated [17,53]. Due to the restriction of the computational power, it is difficult to take a huge grid size in which L is much larger than λ.…”

Section: Initial Condition and Setting For Simulationmentioning

confidence: 99%

Merger of binary neutron stars to a black hole: Disk mass, short gamma-ray bursts, and quasinormal mode ringing

2006

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Three-dimensional simulations for the merger of binary neutron stars are performed in the framework of full general relativity. We pay particular attention to the black hole formation case and to the resulting mass of the surrounding disk for exploring possibility for formation of the central engine of short-duration gamma-ray bursts (SGRBs). Hybrid equations of state are adopted mimicking realistic, stiff nuclear equations of state (EOSs), for which the maximum allowed gravitational mass of cold and spherical neutron stars, M sph , is larger than 2M⊙. Such stiff EOSs are adopted motivated by the recent possible discovery of a heavy neutron star of mass ∼ 2.1 ± 0.2M⊙. For the simulations, we focus on binary neutron stars of the ADM mass M > ∼ 2.6M⊙. For an ADM mass larger than the threshold mass M thr , the merger results in prompt formation of a black hole irrespective of the mass ratio QM with 0.65 < ∼ QM ≤ 1. The value of M thr depends on the EOSs and is approximately written as 1.3-1.35M sph for the chosen EOSs. For the black hole formation case, we evolve the spacetime using a black hole excision technique and determine the mass of a quasistationary disk surrounding the black hole. The disk mass steeply increases with decreasing the value of QM for given ADM mass and EOS. This suggests that a merger with small value of QM is a candidate for producing central engine of SGRBs. For M < M thr , the outcome is a hypermassive neutron star of a large ellipticity. Because of the nonaxisymmetry, angular momentum is transported outward. If the hypermassive neutron star collapses to a black hole after the longterm angular momentum transport, the disk mass may be > ∼ 0.01M⊙ irrespective of QM . Gravitational waves are computed in terms of a gauge-invariant wave extraction technique. In the formation of the hypermassive neutron star, quasiperiodic gravitational waves of frequency between 3 and 3.5 kHz are emitted irrespective of EOSs. The effective amplitude of gravitational waves can be > ∼ 5 × 10 −21 at a distance of 50 Mpc, and hence, it may be detected by advanced laser-interferometers. For the black hole formation case, the black hole excision technique enables a longterm computation and extraction of ring-down gravitational waves associated with a black hole quasinormal mode. It is found that the frequency and amplitude are ≈ 6.5-7 kHz and ∼ 10 −22 at a distance of 50 Mpc for the binary of mass M ≈ 2.7-2.9M⊙.

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“…Preliminary results obtained in [38] suggest that waveforms calculated from a numerical relativity binary inspiral simulation can be done in an accurate fashion (e.g., with errors less than 10%) only when the extraction radius is approximately one gravitational wavelength λ g away from the center of mass of the system (for comparison, the NS-4 calculations from the previous section has the outer boundary at only 0.08λ gw ). However, gravitational wave extraction is just one aspect of our simulation requirements.…”

Section: Long-term General Relativistic Numerical Simulationsmentioning

confidence: 99%

Towards a realistic neutron star binary inspiral: Initial data and multiple orbit evolution in full general relativity

2004

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This paper reports on our effort in modeling realistic astrophysical neutron star binaries in general relativity. We analyze under what conditions the conformally flat quasiequilibrium (CFQE) approach can generate "astrophysically relevant" initial data, by developing an analysis that determines the violation of the CFQE approximation in the evolution of the binary described by the full Einstein theory. We show that the CFQE assumptions significantly violate the Einstein field equations for corotating neutron stars at orbital separations nearly double that of the innermost stable circular orbit (ISCO) separation, thus calling into question the astrophysical relevance of the ISCO determined in the CFQE approach.With the need to start numerical simulations at large orbital separation in mind, we push for stable and long term integrations of the full Einstein equations for the binary neutron star system. We demonstrate the stability of our numerical treatment and analyze the stringent requirements on resolution and size of the computational domain for an accurate simulation of the system.

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Equilibrium and stability of supermassive stars in binary systems

Cited by 35 publications

References 30 publications

Various features of quasiequilibrium sequences of binary neutron stars in general relativity

Various features of quasiequilibrium sequences of binary neutron stars in general relativity

Merger of binary neutron stars to a black hole: Disk mass, short gamma-ray bursts, and quasinormal mode ringing

Towards a realistic neutron star binary inspiral: Initial data and multiple orbit evolution in full general relativity

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